P0139: O2 sensor circuit slow response (bank 1, sensor 2)

How to read it

P0139 is one of the standard OBD-II trouble codes stored when the check engine light comes on. SAE J2012, the standard that defines the codes, names it “O2 Sensor Circuit Slow Response Bank 1 Sensor 2”; Volkswagen’s service information gives the same name.

Also searched as: code P0139, P0139 code.

What the monitor checks

The federal rule requires the system to detect oxygen sensor deterioration or malfunction that raises emissions to 1.5 times the standard.

What the manual says to do

Ford’s F-150 manual says that if the indicator stays on, the vehicle should be serviced at the first available opportunity, and that continued driving with it on can mean higher emissions, lower fuel economy, rougher running and more costly repairs.

How the light goes out

Under the federal rule, the check engine light may go out once the fault has not come back during three trips in a row in which its monitor runs without finding it. The system may erase the stored code if the same code has not been registered again in at least 40 engine warm-up cycles.